1. Field of the Invention
The present invention relates to an upper substrate and a liquid crystal display apparatus (LCD) having the upper substrate, and more particularly to an upper substrate for enhancing display quality and a liquid crystal display apparatus having the upper substrate.
2. Description of Related Art
FIG. 1 is a cross-sectional view of a conventional liquid crystal display apparatus and FIG. 2 is an output signal pattern of gate-driving circuit shown in FIG. 1. In FIG. 2, x-axis represents time and y-axis resents voltage.
Referring to FIG. 1, a conventional liquid crystal display apparatus 40 includes a lower substrate 10 or an array substrate 10, an upper substrate 20 or a color filter substrate 20 and a liquid crystal layer 30 interposed between the array substrate 10 and the color filter substrate 20. Electric field is formed between the color filter substrate 20 and the array substrate 10, and aligning angles of the liquid crystal molecules of the liquid crystal layer 30 are changed by the electric field, so that the liquid crystal display apparatus 40 displays an image of external signal. The array substrate 10 includes a display region DA and a peripheral region PA adjacent to the display region DA. A display part for displaying an image is disposed at the display region DA, and a driving part for driving the display part is disposed at the peripheral region PA.
The display region DA includes a plurality of pixels arranged in a matrix shape. Each of the pixels includes a gate line, a data line, a thin film transistor (TFT) 11 that is electrically connected to the gate line and the data line, and a pixel electrode 12 electrically connected to the thin film transistor 11.
A gate driving circuit 16 that applies drive voltage to the gate line is formed in the peripheral region PA through a process of forming thin film transistor. Forming the gate driving circuit 16 in the peripheral region PA reduces a number of processes of manufacturing the liquid crystal display apparatus 40, and volume and a size of the liquid crystal display apparatus 40.
A common electrode 24 of the color filter substrate 20 is formed to face the pixel electrode 12 of the display region DA and the liquid crystal layer 30 is interposed between the common electrode 24 and the pixel electrode 12. A cell gap retaining member 25 is formed on the common electrode 24 for retaining the cell gap of the liquid crystal display apparatus 40.
Since the common electrode 24 also faces the gate driving circuit 16 of the peripheral region PA and the liquid crystal layer 30 is interposed between them, there exists a parasitic capacitance between the gate driving circuit 16 and the common electrode 24.
In FIG. 2, a solid line A1 is a normal curve, whereas the dotted line A2 is a distorted curve caused by the parasitic capacitance between the gate driving circuit 16 and the common electrode 24. FIG. 2 shows that maximum point of voltage of the distorted curve is at least 5V lower than that of the normal curve.
According to FIG. 2, the parasitic capacitance causes a distortion and a delay of output signal of gate driving circuit 16, and eventually deterioration of the display quality of liquid crystal display apparatus 40.
Further, when external forces applied to the peripheral region PA, the common electrode 24 and the gate driving circuit 16 may be electrically shorted to cause malfunction of the gate driving circuit 16.